Charge-Transfer Excitons in Coupled Atomically Thin Polar Nitride Quantum Wells

Due to their extended lifetimes relative to those of spatially direct excitons (DXs), spatially indirect excitons (IXs) open new avenues for exploring excitonic devices and fundamental excitonic phenomena. Atomically thin nitride quantum heterostructures are a promising platform for realizing strongly bound IXs because they exhibit large exciton binding energies due to extreme quantum confinement and a strong polarization field. We apply first-principles calculations to investigate the properties of excitons in pairs of atomically thin GaN quantum wells separated by polar AlN layers with varying thicknesses. We show that the degree of electron-hole interaction and exciton character (IX or DX) can be controlled by changing the AlN barrier thickness and polarization, enabling IXs with radiative decay rates significantly lower than those of DXs. Our theoretical findings predict the feasibility of room-temperature-stable excitons in a commercial semiconductor platform. Furthermore, we present the first experimental results that demonstrate the successful growth of these atomically thin nitride heterostructures.